1. Field of the Invention
The present invention relates generally to a lens apparatus and particularly but not exclusively to a lens apparatus using autofocus detection.
2. Description of the Related Art
Conventionally, an autofocus detection (referred to as AF below) control system has been essential in an image capturing apparatus such as a general-use video camera. In conventional lens apparatuses employing such AF systems (e.g. European Patent Publication No. EP-A2-762742), can be a signal can be extracted from captured images and evaluated in accordance with a sharpness of an object so as to detect a focal point of an optical system.
Conventional lens apparatuses employing the above-mentioned AF system are shown in FIGS. 14 and 15.
First, the conventional lens apparatus shown in FIG. 14 will be described.
Referring to FIG. 14, reference numeral 11 denotes an interchangeable lens unit; numeral 200 a camera; and numeral 300 a coaxial cable. In the camera 200, a process unit 1202 processes an output signal from a CCD 1201 and formats it to an National Television System Committee (NTSC) signal. A record reproducing unit 1203 records an image signal produced from the process unit 1202 on a recording medium. An output switching unit 1204 selects an image signal output from the process unit 1202 and the record reproducing unit 1203. An image output terminal 1205 outputs an image signal received from the output switching unit 1204.
In the lens unit 11, an image input terminal 1100 receives an image signal (e.g., via a coaxial cable 300). An evaluation value producing unit 1101 extracts a sharpness evaluation value 1111 from the image signal received from the image input terminal 1100. An AF drive controller 1102 produces a motor control signal, where the motor control signal is configured to maximize the sharpness evaluation value 1110 produced in the evaluation value producing unit 1101. A motor 1103 is controlled from the AF drive controller 1102, and a focus lens 1104 is moved in an optical axial direction by the driving of the motor 1103.
Operation of the conventional lens apparatus system of FIG. 14 will be described.
A beam passed through a focus lens 1104 forms an image on an image capturing surface of the CCD 1201, which in turn enters the process unit 1202 by sample-holding after being photo-electrically converted. In the process unit 1202, an input signal is processed to an image format such as the NTSC signal so as to be sent to the output switching unit 1204 and the record reproducing unit 1203.
During image recording, in the output switching unit 1204, the output of the process unit 1202 can be received by the image output terminal 1205, and the record reproducing unit 1203 records the output of the process unit 1202 on a recording medium.
During reproducing, the record reproducing unit 1203 reproduces the image signal recorded on a recording medium, and when the image signal is stably reproduced, the output switching unit 1204 outputs the image signal of the record reproducing unit 1203 to the image output terminal 1205.
To the image input terminal 1100 of the lens unit 11, an image signal is received from the image output terminal 1205 of the camera 200 via the coaxial cable 300. The image signal received in the image input terminal 1100 is filtered in the evaluation value producing unit 1101. The filtering produces a sharpness evaluation value, related to image frequency components in a vertically synchronized cycle unit of the image signal, which is sent to the AF drive controller 1102. In the AF drive controller 1102, a motor control signal is produced so as to move the focus lens 1104 to a position where the sharpness evaluation value 1111 is increased. The motor control signal is created by sequentially comparing, sharpness evaluation value 1111 in a vertically synchronizing cycle unit, the sharpness evaluation value 1111 to the required motor motion to increase the sharpness evaluation value 1111. The motor 1103 is driven by the motor control signal, thereby moving the focus lens 1104 to an in-focus point.
An example of a conventional AF driving operation will be described. First, it is determined whether the in-focus point is located at a position remote from or close to the present position of the focus lens 1104 by evaluating changes in sharpness evaluation value 1111 when the focus lens 1104 is slightly moved. This in turn determines a driving direction. Then, in order to detect the peak value of the sharpness evaluation, the focus lens 1104 is moved according to the determination result of the driving direction at a certain speed. This is referred to as a mountain-climbing determination. After the peak value is passed, by reversing the driving direction, the focus lens 1104 is moved in very small increments so as to increase the sharpness evaluation value 1111. This is referred to as a peak determination. After the peak determination, the sharpness evaluation value 1111 is compared with the value directly after the peak determination, so that when the value changes, the AF operation is restarted.
Next, the conventional lens apparatus shown in FIG. 15 will be described.
Referring to FIG. 15, reference numeral 11 denotes an interchangeable lens unit; numeral 210 a camera; and numeral 300 the coaxial cable.
In the camera 210, the process unit 1202 processes an output signal from the CCD 1201 and formats it to an NTSC signal. An image capturing/reproducing switching input unit 1206 establishes the operation of the camera 210 in an image capturing mode or a reproducing mode. The record reproducing unit 1203 determines whether to reproduce the image signal recorded on a recording medium depending upon the mode of the image capturing/reproducing switching input unit 1206. An output switching unit 1204 selects an image signal output from the process unit 1202 and the record reproducing unit 1203, the image signal affected by the mode of the image capturing/reproducing switching input unit 1206. The image output terminal 1205 receives the image signal from the output of the output switching unit 1204.
In the lens unit 11, the image input terminal 1100 receives an image signal via the coaxial cable 300, and the evaluation value producing unit 1101 extracts a sharpness evaluation value 1111 from the image signal received by the image input terminal 1100. The AF drive controller 1102 produces a motor control signal so as to maximize the sharpness evaluation value 1111 produced in the evaluation value producing unit 1101. The motor 1103 is controlled from the AF drive controller 1102, where the motor 1103 drives the movement of the focus lens 1104 in an optical axial direction.
Operation of the conventional lens apparatus shown in FIG. 15 will be described.
A beam passed through the focus lens 1104 forms an image on an image capturing surface of the CCD 1201, which is photo-electrically converted and stored, the stored Value entering the process unit 1202. In the process unit 1202, an input signal is processed to an image format such as the NTSC signal so as to be sent to the output switching unit 1204 and the record reproducing unit 1203.
Operations in the output switching unit 1204 and the record reproducing unit 1203 follow the mode of the image capturing/reproducing switching input unit 1206. That is, during image capturing, the output switching unit 1204 sends the output of the process unit 1202 to the image output terminal 1205.
During reproducing, the record reproducing unit 1203 reproduces the image signal recorded on a recording medium, and when the image signal is stably reproduced, the output switching unit 1204 sends the image signal of the record reproducing unit 1203 to the image output terminal 1205.
The image input terminal 1100 of the lens unit 11, receives an image signal from the image output terminal 1205 of the camera 210 via the coaxial cable 300. The image signal received in the image input terminal 1100 is filtered in the evaluation value producing unit 1101. The filtering produces a sharpness evaluation value 1111, related to image frequency components in a vertically synchronizing cycle unit of the image signal, which is sent to the AF drive controller 1102. In the AF drive controller 1102, a motor control signal is produced so as to move the focus lens 1104 to a position where the sharpness evaluation value 1111 is maximized. The motor control signal is created by sequentially comparing, in a vertically synchronizing cycle unit, the sharpness evaluation value 1111 to the required motor motion to increase the sharpness evaluation value 1111. The motor 1103 is driven, by the motor control signal, thereby moving the focus lens 1104 to an in-focus point.
According to the conventional lens apparatus shown in FIG. 14, the sharpness evaluation value 1111 is produced by the CCD 1201 and the process unit 1202 after the focus lens 1104 is driven. However a delay is generated between the measured sharpness evaluation value 1111 and the corresponding focus lens position.
In order to overcome such a delay, during the direction determination, it is necessary to use a sharpness evaluation value 1111 entered for use in the determination after the focus lens 1104 is very slightly moved in view of the delay in time. Such an attention to the delay in time may also be necessary during the peak determination.
As described above, in the conventional lens apparatus, the time delay in the AF operation is required in order to achieve a camera unit capable of the AF operation whenever the lens 100 is replaced. However the delay time of the camera 200 (210) cannot be uniquely established. As the digitalization of the camera 200 (210) further progresses, additional delay contributors (e.g. memory), may exist inside the process unit 1202, and the additional time delay contributors can vary depending on the camera model. Thus, making it difficult to more accurately reflect the delay time differences related to AF operation in various camera models.
According to the conventional lens apparatus shown in FIG. 15, because the image capturing/reproducing modes are not communicated between the lens unit 11 and the camera 210, even when the camera 210 is in the reproducing mode, the lens unit 11 is AF-operated for the received reproducing image.
As a result, the focus lens 1104 is driven so as to consume electric power in vain. As a countermeasure, the image capturing/reproducing modes may communicate between the lens unit 11 and the camera 200 in the content a special communication; however, in order to achieve a camera unit capable of the AF operation, whenever the lens unit 11 is replaced, it is difficult to control the accuracy of the content of the special communication of the image capturing/reproducing modes.